This invention relates to a chemically amplified positive resist composition having a high resolution, dry etching resistance, and minimized slimming of a pattern film after development, and useful as a micropatterning material especially for the manufacture of VLSI.
It also relates to a chemically amplified positive resist composition for forming a contact hole pattern by the thermal flow process. While a method for forming a contact hole pattern using a chemically amplified positive resist composition comprising a polymer as the base resin involves the thermal flow step of heat treating the contact hole pattern for further reducing the size of contact holes, the invention relates to the resist composition to which a compound having functional groups capable of crosslinking with the polymer is added so that the size reduction by thermal flow becomes easy to control. The invention further relates to a method for forming a microsize contact hole pattern in the manufacture of VLSIs.
While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet, EB, EUV and x-ray lithography is thought to hold particular promise as the next generation in microfabrication technology. Deep-UV lithography is capable of achieving a minimum feature size of 0.3 xcexcm or less and, when a resist having low light absorption is used, can form patterns with sidewalls that are nearly perpendicular to the substrate.
Recently developed acid-catalyzed chemically amplified positive resists, such as those described in JP-B 2-27660, JP-A 63-27829, U.S. Pat. No. 4,491,628 and U.S. Pat. No. 5,310,619, utilize a high-intensity KrF or ArF excimer laser as the deep-UV light source. These resists, with their excellent properties such as high sensitivity, high resolution, and good dry etching resistance, are especially promising for deep-UV lithography.
Such chemically amplified positive resist compositions include two-component systems comprising a base resin and a photoacid generator, and three-component systems comprising a base resin, a photoacid generator, and a dissolution regulator having acid labile groups.
For example, JP-A 62-115440 describes a resist composition comprising poly-4-tert-butoxystyrene and a photoacid generator, and JP-A 3-223858 describes a similar two-component resist composition comprising a resin bearing tert-butoxy groups within the molecule, in combination with a photoacid generator. JP-A 4-211258 describes a two-component resist composition which is comprised of polyhydroxystyrene bearing methyl, isopropyl, tert-butyl, tetrahydropyranyl, and trimethylsilyl groups, together with a photoacid generator. JP-A 6-100488 discloses a resist composition comprising a polydihydroxystyrene derivative, such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene] or poly[3,5-bis(2-tetrahydropyranyloxy)styrene], and a photoacid generator. These resists, however, have the drawbacks of slimming of a pattern film after development with an aqueous base solution and poor resistance to dry etching.
Also known in the art are resist compositions using copolymers of hydroxystyrene with (meth)acrylate for achieving a higher transparency and improving the adhesion to the substrate as disclosed in JP-A 8-101509 and 8-146610. The resist compositions of this type suffer from low heat resistance, partial pattern collapse, and pattern shape footing.
Improvement and development efforts have been continuously made on the base resin in resist compositions of this type. JP-A 10-207066 discloses a resist composition comprising a base resin which is crosslinked with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages and a photoacid generator wherein the crosslinking groups are eliminated under the action of acid generated from the photoacid generator upon exposure, achieving a high contrast and high resolution.
Even when any base resin designed to enhance the resolving power is used in such chemically amplified positive resist compositions, it is yet difficult to reach a contact hole size of 0.20 xcexcm or less. There are available no resist compositions for forming a contact hole pattern satisfying the requirement of LSI devices of the next generation.
On the other hand, the known technology of forming a contact hole size of 0.20 xcexcm or less is to heat treat a contact hole pattern for causing the resist film to flow and reducing the contact hole size. This technology is known as thermal flow process. The use of the thermal flow process enables formation of a miniature contact hole size as fine as 0.10 xcexcm or 0.15 xcexcm.
In forming microsize contact holes by the thermal flow process, however, it is very difficult to control the heat treating temperature so as to provide a shrinkage matching with the desired contact hole size. That is, the thermal flow process has the drawback that even a slight variation of heating temperature brings about a substantial variation of contact hole size.
Referring to FIG. 1, there is illustrated in cross section a resist film 2 on a substrate 1, a contact hole 3 being formed through the resist film 2. The contact hole having undergone the thermal flow process has a profile as shown in FIG. 1, that is, a cross-sectional profile bowed at corners. The thermal flow process also has the problem that the profile of a contact hole is deteriorated.
An object of the invention is to provide a chemical amplification type, positive working resist composition which has a higher sensitivity, resolution, dry etching resistance and process adaptability than conventional resist compositions, and is improved in the slimming of a pattern film after development with an aqueous base solution.
Another object of the invention is to provide a novel and improved chemical amplification type, positive working resist composition which has controllable process adaptability relative to the heat treating temperature when a microsize contact hole pattern is conventionally formed by the thermal flow process, and thus has satisfactory practical utility. A further object is to provide a novel and improved method for forming a contact hole pattern.
It has been found that using a chemically amplified positive resist composition comprising a compound containing at least two functional groups of the general formula (1) in a molecule, a resist pattern can be formed with the advantages of improved process control and practical utility. 
Herein R1 to R4 are hydrogen or straight, branched or cyclic alkyl groups of 1 to 12 carbon atoms, and a pair of R1 and R3, or a pair of R2 and R3, taken together, may form a ring.
When only a polyhydroxystyrene derivative is formulated in a resist composition as the base resin, there arise such drawbacks as slimming of a pattern film after development with an aqueous base solution and poor dry etching resistance. Even when a copolymer of hydroxystyrene with (meth)acrylate is formulated in a resist composition as the base resin, the above drawbacks are not fully overcome. It has been found that an allyloxy compound having at least two functional groups of formula (1) in a molecule is an effective additive to a chemically amplified positive resist composition, and more specifically, that a chemically amplified positive resist composition comprising the allyloxy compound, a polymer, a photoacid generator and an organic solvent has a high sensitivity, high resolution, dry etching resistance, and process adaptability, and is improved in the slimming of a pattern film after development with an aqueous base solution. The composition is thus well suited for practical use and advantageously used in precise microfabrication, especially in VLSI manufacture. When a vinyloxy compound is added in an analogous way, similar effects are exerted, but accompanied by such drawbacks as a number of foreign particles in the pattern formed and the lack of storage stability. The addition of the allyloxy compound substantially precludes the appearance of such drawbacks.
It has also been found that the allyloxy compound containing at least two functional groups of the formula (1) in a molecule is effective for reducing the flow rate associated with the thermal flow process and that using a chemically amplified positive resist composition comprising the allyloxy compound, a method for forming a contact hole pattern according to the thermal flow process is given the advantages of effective process control and practical utility.
Specifically, making the investigations to be described below, the inventor has established the method of controlling the thermal flow process.
In the inventor""s experiment, a variety of base resins commonly used in conventional chemically amplified positive resist compositions were used to form resist films, which were provided with contact holes and subjected to the thermal flow process. The contact hole size was plotted relative to the heating temperature in a graph. It was found that the slope representing a change of contact hole size (to be referred to as a flow rate, hereinafter) was not so different among different base resins. Namely, changing the base resin skeleton gives no substantial difference in the flow rate. The flow rate remains substantially unchanged whether the base resin is a homopolymer or a copolymer and when the molecular weight or dispersity of the base resin is changed. This is also true when the acid labile group and other substituents are changed. The flow rate does not depend on the percent and type of substitution. Blending two or more distinct polymers brings little change of the flow rate. Through these investigations, it was found that only the flow initiation temperature, that is, the temperature at which the contact hole size becomes reduced changes with the base resin and depends on the glass transition temperature (Tg) of the base resin.
A summary of these findings can be illustrated in the graph of FIG. 2. In FIG. 2, curve I denotes a low molecular weight polymer, curve II denotes polymer A, curve III denotes polymer B, curve IV denotes a blend of polymer A and polymer B, curve V denotes a polymer having crosslinking groups, curve VI denotes a high molecular weight polymer, and curve VII denotes a polymer having a high Tg. The gradient of the curve represents the flow rate.
The flow rate can be numerically represented by a change of the contact hole size per degree centigrade of the heating temperature (unit: nm/xc2x0 C.). While the base resin was changed among a variety of polymers, the flow rate did not substantially change. The change of contact hole size per degree centigrade was approximately 20 nm/xc2x0 C. In the fabrication of LSI devices of the next generation targeting further miniaturization, the flow rate of 20 nm/xc2x0 C. is difficult to control, inadequate to process adaptability, and by no means permissible.
Based on the above findings, the inventor made further investigations to find that when a contact hole pattern is formed by the thermal flow process using a chemically amplified positive resist composition comprising a compound containing at least two functional groups of the general formula (1) in a molecule, there are achieved a reduced flow rate, improved process control and practical utility.
By adding a compound containing at least two functional groups of the general formula (1) in a molecule to a chemically amplified positive resist composition, the flow rate in the thermal flow process, that is, the change of contact hole size per degree centigrade of heating temperature is improved as demonstrated in the graph of FIG. 3. In FIG. 3, curve A denotes a composition having the relevant compound added thereto and curve B denotes a control composition (free of the relevant compound).
It is believed that when the compound containing at least two functional groups of the general formula (1) in a molecule is formulated together with a base resin in a chemically amplified positive resist composition, thermal crosslinking reaction can take place between the functional groups and the base resin. It is generally unknown that the functional groups of formula (1), designated allyloxy groups, undergo thermal crosslinking reaction with the base resin in the chemically amplified positive resist composition. Although it is known that compounds having at least two alkenyloxy groups such as vinyloxy, isopropenyloxy and isobutenyloxy groups readily undergo thermal reaction with hydroxyl groups on the base resin in the chemically amplified positive resist composition to form acetal bonds for crosslinking, it is unknown that compounds having functional groups of formula (1) undergo similar reaction. It is considered that the functional groups of formula (1) undergo transition reaction within the resist film to form alkenyloxy groups, thereby incurring similar crosslinking reaction as mentioned above or that the functional groups of formula (1) directly react with benzene rings or polymer chains of the resist base resin to form crosslinks. It has been empirically found that when the compound containing at least two functional groups of formula (1) is added to a chemically amplified positive resist composition, thermal crosslinking reaction proceeds at the heat treating temperature during the thermal flow process, interfering with the rate at which the resist film is fluidized and thereby reducing the flow rate of contact holes. It is also appreciated that the compounds having functional groups of formula (1) are easier to prepare and commercially available at a lower cost than the compounds having alkenyloxy groups such as vinyloxy groups.
After a chemically amplified positive resist composition having added thereto the compound containing at least two functional groups of the general formula (1) in a molecule added thereto was used to form a resist film, which was provided with contact holes and subjected to the thermal flow process, the resulting contact hole pattern configuration was observed. The contact hole pattern was improved in perpendicularity, as compared with a control resist composition (without the compound containing at least two functional groups of formula (1)) yielding a contact hole pattern having rounded sidewalls at the end of thermal flow.
In summary, it has been found that the addition of the compound containing at least two functional groups of the formula (1) is effective for reducing the flow rate associated with the thermal flow process of forming a microsize contact hole pattern and that the composition is effectively controllable and process adaptable in the fabrication of LSI devices of the next generation targeting further miniaturization.
In a first aspect, the invention provides a chemically amplified positive resist composition comprising a compound containing at least two functional groups of the general formula (1) in a molecule. 
Herein R1 to R4 are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 12 carbon atoms, and a pair of R1 and R3, or a pair of R2 and R3, taken together, may form a ring.
Preferably, the compound containing at least two functional groups has the general formula (2). 
Herein Z is a functional group of the formula (1), the Z""s may be the same or different, k is a positive integer of 2 to 6, and X is a k-valent organic group of 2 to 20 carbon atoms. The compound of the formula (2) is preferably present in an amount of 0.1 to 5% by weight of the overall resist composition.
Typically, the resist composition is used for forming a contact hole pattern by the thermal flow process.
In a second aspect, the invention provides a chemically amplified positive resist composition for forming a contact hole pattern by the thermal flow process, comprising
(A) an organic solvent,
(B) a base resin in the form of a polymer having acid labile groups,
(C) a photoacid generator,
(D) a basic compound, and
(E) the compound containing at least two functional groups of the general formula (1) in a molecule.
In one preferred embodiment, the base resin (B) is a polymer comprising recurring units of the following general formula (3) in which some of the hydrogen atoms of the phenolic hydroxyl groups are partially replaced by acid labile groups of at least one type, and some of the hydrogen atoms of the remaining phenolic hydroxyl groups are optionally eliminated for crosslinkage within a molecule and/or between molecules with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages, the total of the acid labile groups and the crosslinking groups being more than 0 mol % to 80 mol % of the entire hydrogen atoms of phenolic hydroxyl groups in the formula (3). The polymer has a weight average molecular weight of 1,000 to 500,000.
Herein R5 is hydrogen or methyl, R6 is hydrogen or a methyl, phenyl or cyano group, R7 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, R8 is hydrogen, a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, or an acid labile group, x and y each are 0 or a positive integer of up to 5, z is an integer satisfying y+zxe2x89xa65, m and p are 0 or positive numbers, n is a positive number, satisfying 0xe2x89xa6m/(m+n+p)xe2x89xa60.8, 0 less than n/(m+n+p)xe2x89xa61, and 0xe2x89xa6p/(m+n+p)xe2x89xa60.8.
In a further preferred embodiment, the base resin (B) is a polymer represented by the following general formula (4), that is a polymer comprising recurring units of the general formula (3) in which some of the hydrogen atoms of the phenolic hydroxyl groups are partially replaced by acid labile groups of at least one type, and some of the hydrogen atoms of the remaining phenolic hydroxyl groups are optionally eliminated for crosslinkage within a molecule and/or between molecules with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages, the total of the acid labile groups and the crosslinking groups being more than 0 mol % to 80 mol % of the entire hydrogen atoms of phenolic hydroxyl groups in formula (3). The polymer has a weight average molecular weight of 
1,000 to 500,000.
A is a group of the following formula (4a). 
Herein R5 is hydrogen or methyl, R6 is hydrogen or a methyl, phenyl or cyano group, R7 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, R8 is hydrogen, a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, or an acid labile group, R9 is an acid labile group of at least one type, R10, R11, R13 and R14 are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 6 carbon atoms, R12 is a xcexa-valent aliphatic or alicyclic saturated hydrocarbon, aromatic hydrocarbon or heterocyclic group of 1 to 50 carbon atoms which may be separated by a hetero atom, and in which some hydrogen atoms attached to carbon atoms may be replaced by hydroxyl groups, carboxyl groups, carbonyl groups or halogen atoms, and xcexa is an integer of 2 to 5,
each unit may be constructed of one type or at least two types,
x and y each are 0 or a positive integer of up to 5, z is an integer satisfying y+zxe2x89xa65, a and b are 0 or positive integers, c is a positive integer, satisfying a+b+cxe2x89xa65, d, e and f are 0 or positive integers satisfying d+e+fxe2x89xa64,
q, s, t and u are 0 or positive numbers, r is a positive number, satisfying 0xe2x89xa6q/(q+r+s+t+u)xe2x89xa60.8, 0 less than s/(q+r+s+t+u)xe2x89xa60.8, 0xe2x89xa6t/(q+r+s+t+u)xe2x89xa60.8, 0xe2x89xa6u/(q+r+s+t+u)xe2x89xa60.8, 0 less than (r+s+t)/(q+r+s+t+u)xe2x89xa61, and 0 less than r/(q+r+s+t+u)xe2x89xa60.8.
In a still further preferred embodiment, the base resin (B) is a polymer represented by the following general formula (5), that is a polymer comprising recurring units of the general formula (3) in which some of the hydrogen atoms of the phenolic hydroxyl groups are partially replaced by acid labile groups of at least one type, and some of the hydrogen atoms of the remaining phenolic hydroxyl groups are optionally eliminated for crosslinkage within a molecule and/or between molecules with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages, the total of the acid labile groups and the crosslinking groups being more than 0 mol % to 80 mol % of the entire hydrogen atoms of phenolic hydroxyl groups in formula (3). The polymer has a weight average molecular weight of 1,000 to 500,000.
Herein R5, R6, R7, R8, R9, R10, R11, A, x, y, z, a, b, c, d, e, and f are as defined above,
R15 and R16 are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 8 carbon atoms, R17 is a monovalent hydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom, a pair of R15 and R16, a pair of R15 and R17 or a pair of R16 and R17, taken together, may form a ring, each of R15, R16 and R17 is a straight or branched alkylene group of 1 to 8 carbon atom when they form a ring, R18 is a tertiary alkyl group of 4 to 20 carbon atoms,
g is 0 or a positive integer of 1 to 6, q, s1, s2, s3, t and u are 0 or positive numbers, r is a positive number, satisfying
0xe2x89xa6q/(q+r+s1+s2+s3+t+u)xe2x89xa60.8,
0xe2x89xa6s1/(q+r+s1+s2+s3+t+u)xe2x89xa60.8,
0xe2x89xa6s2/(q+r+s1+s2+s3+t+u)xe2x89xa60.8,
0xe2x89xa6s3/(q+r+s1+s2+s3+t+u)xe2x89xa60.8,
0 less than (s1+s2+s3)/(q+r+s1+s2+s3+t+u)xe2x89xa60.8,
0xe2x89xa6t/(q+r+s1+s2+s3+t+u)xe2x89xa60.8,
0xe2x89xa6u/(q+r+s1+s2+s3+t+u)xe2x89xa60.8,
0 less than (r+s1+s2+s3+t)/(q+r+s1+s2+s3+t+u)xe2x89xa61, and
0 less than r/(q+r+s1+s2+s3+t+u)xe2x89xa60.8.
Preferably, component (C) is an onium salt and/or diazomethane derivative, and component (D) is an aliphatic amine.
In a third aspect, the invention provides a method for forming a contact hole pattern, comprising the steps of (i) applying the chemically amplified positive resist composition of any one of claims 4 to 10 onto a substrate to form a coating, (ii) heat treating the coating and exposing the coating to high energy radiation with a wavelength of up to 300 nm or electron beam through a photo-mask, (iii) optionally heat treating the exposed coating, and developing the coating with a developer, thereby forming a contact hole pattern, and (iv) further heat treating the contact hole pattern for reducing the size of contact holes.
In another preferred embodiment, the resist composition of the first aspect further includes as the base resin a polymer comprising recurring units of the following general formula (6) or (7). 
F is a group of the following formula (6a). 
Herein R is a hydroxyl or OR9 group, R5 is hydrogen or methyl, R7 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, R9, R9a and R9b each are an acid labile group, R10a and R10b each are methyl or ethyl, R12 is a xcexa-valent aliphatic or alicyclic saturated hydrocarbon, aromatic hydrocarbon or heterocyclic group of 1 to 50 carbon atoms which may be separated by a hetero atom, and in which some hydrogen atoms attached to carbon atoms may be replaced by hydroxyl groups, carboxyl groups, carbonyl groups or halogen atoms, and xcexa is an integer of 2 to 5, x is 0 or a positive integer, y is a positive integer satisfying x+yxe2x89xa65, m is 0 or a positive integer, n is a positive integer satisfying m+nxe2x89xa65, a, b, c and d are 0 or positive numbers satisfying a+b+c+d=1.
G is a group of the following formula (7a). 
Herein R5, R6a and R6b each are hydrogen or methyl, R10a and R10b each are methyl or ethyl, R12 is a xcexa-valent aliphatic or alicyclic saturated hydrocarbon, aromatic hydrocarbon or heterocyclic group of 1 to 50 carbon atoms which may be separated by a hetero atom, and in which some hydrogen atoms attached to carbon atoms may be replaced by hydroxyl groups, carboxyl groups, carbonyl groups or halogen atoms, and xcexa is an integer of 2 to 5, R8a is a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain an oxygen or sulfur atom, R8b is a tertiary alkyl group of 4 to 20 carbon atoms, i is a positive integer of up to 5, e, f, g and h each are 0 or a positive number satisfying e+f+g+h=1.
In this regard, the invention also provides a chemically amplified positive resist composition comprising
(a) an organic solvent,
(b) the polymer of formula (6) or (7) as a base resin,
(c) a photoacid generator,
(d) a basic compound, and
(e) the compound of formula (2).